It was a thing with the Joneses. But all of the Joneses were auto dealers.

General Motors Corp.'s Chevrolet Division had the Blazer and the Suburban, and those sport-utility vehicles were selling well.

Oldsmobile dealers noticed, and they wanted one, too. So GM gave them the more upscale Bravada sport-utility vehicle, which didn't sell as well as the Blazer and Suburban, but succeeded in making the company's GMC truck dealers jealous.

So GM gave the GMC dealers a fancy version of the Blazer, the GMC Envoy, which also was based on the Blazer-like GMC Jimmy.

That upset the Cadillac dealers, who wanted a luxury truck of their own.

A sport-utility vehicle with a Cadillac badge! People laughed at the idea at auto shows in Detroit, New York and Los Angeles.

That was a couple of years ago. Today, no one is laughing at Cadillac's Escalade, a plusher-than-thou sport-utility vehicle outfitted with leather and wood and a $46,000 price tag--and that has no shortage of buyers.

Now, get ready for a BMW sport-utility vehicle--the BMW X5, a model designed to compete against Toyota Motor Co.'s luxury Lexus RX 300 in the $35,000 range. BMW, one of the world's premier manufacturers of luxury sports cars, had long eschewed the idea of producing something as clumsy as a truck. But the company couldn't resist the pressure.

Now, many in the industry are betting that even Germany's Porsche--maker of the famed 911 Carrera and 911 Carrera 4 sports cars--will next take the plunge.

What's driving the development of the super trucks--luxury sport-utility vehicles, pickups and, for that matter, minivans equipped with navigational systems, televisions and telephones?

"There are a lot of people out there with a lot of money who want the latest, the biggest and the best," said Jacques DaCosta, senior manager of product research for J.D. Power and Associates, a global market research firm based in Agoura Hills, Calif.

"It's a bizarre phenomenon with no end in sight," DaCosta said.

Sport-utility vehicles, as a group, account for 18.05 percent of all new vehicles sold in the United States, according to the latest J.D. Power figures. That's up from a 9.5 percent market share in 1993.

Mid-size sport-utility models, such as the Ford Explorer and Isuzu Rodeo, account for 10.61 percent of new-vehicle sales. But, lately, their sales have been flat and in need of help from generous consumer incentives and some luxury spiffs, such as leather, wood and video sets.

On the other hand, sales of small sport-utility models, such as the Honda CR-V and Toyota RAV-4, have been growing. Their sales are up 26.3 percent this year, giving them a 2.62 percent share of the overall new-vehicle market.

Sales of full-size sport-utility models, such as the Chevrolet Tahoe, also are rising, up 11 percent so far this year, giving them a 3.52 percent market share.

But it's the rich sport-utilities, highlighted by models such as the Escalade, the Lexus LX 470 and RX 300, and the humongous new "bigger-than-a-Chevy Suburban" Ford Excursion, that have captured the national attention and imagination. They start at around $35,000.

Luxury sport-utility vehicle sales are up 35.4 percent this year, though their actual overall new-vehicle market share is a tiny 1.3 percent.

But they have a value beyond their actual numbers. The auto industry reveres rich trucks as "halo vehicles," largely because of their ability to attract buyers' attention, including the vast majority of buyers who settle for less expensive models.

That halo effect comes as much from the actual buyers of rich trucks as it does from the trucks themselves, analysts say.

Take a look at the demographics. Rich truck owners have a median annual household income of $140,000. Their average age is 48 years. About 55 percent of them are male. They are entrepreneurs, actors, athletes, publishers, general movers and shakers. Retailers absolutely love them.

It is no wonder, then, that DaimlerChrysler AG spent several hundred million dollars setting up a plant in Vance, Ala., to build its luxury Mercedes-Benz M-Class sport-utility models. And what about those?

DaimlerChrysler at first planned to offer an "affordable" model, the V-6 powered ML320, to compete with high-end Ford Explorer and Jeep Grand Cherokee sport-utility vehicles sold in the $35,000 range.

The ML320 was a hit. The Alabama plant could barely keep up with demand. But well-off consumers clamored for an even more powerful, more luxurious model with the Mercedes-Benz badge. DaimlerChrysler came up with the 268-horsepower, V-8 Mercedes-Benz ML430 for a price of about $44,000.

It's tough keeping up with the Joneses.

The Mid-Level Squeeze

While mid-range sport-utility vehicles are still the most popular choice for those buying SUVs . . .

Market share of light truck sales 1999 (through August)

Mid-size* SUV: 10.6%

Full-size SUV: 3.5%

Mini SUV: 2.6%

Luxury SUV: 1.3%

*Also known as compact

. . . sales for luxury and compact SUVs have increased much faster than those of mid-size ones.

Percent change in sales 1998 to 1999 (through August)

Luxury SUV: 35.4%

Mini SUV: 26.3%

Mid-size SUV: 14.2%

Full-size SUV: 11.0%

SOURCE: J.D. Power and Associates